Touch screen displays for computing devices have recently become quite popular, especially for small, portable devices such as mobile cellular telephone devices. The touch screen allows a user to interact with displayed content as well as to enter input without the need of conventional computing input devices such as, for example, a keyboard or mouse. As a result, there has been much attention given to the design and use of touch screen displays.
One area of interest that can broaden the user experience of using a touch screen display is force sensing. Force sensing determines not only where on the screen the user is touching, but also the force being used by the user in interacting with the touch screen display. The amount of force used can be used by the device to modify content being displayed on the touch screen display in correspondence with the amount of force.
In a conventional touch screen, for example, location of a touch can be sensed based on electrical changes (i.e. capacitive, resistive). The magnitude of the change, so long as it exceeds some threshold, is of less, if any, concern. Force sensing, however, requires a determination of the amount of change. Given that transparent conductor material used in touch screens, such as, for example, indium tin oxide, is typically sputter deposited, there is an inherent and significant tolerance variation in the process. The process variations can result in substantially different electrical properties from unit to unit, which affects the determination of the magnitude of force applied to the touch screen.
Accordingly, there is a need for a method to account for process variations in force-sensing touch screen panels so that a similar user experience occurs from unit to unit despite such variations.
Those skilled in the field of the present disclosure will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Well known elements, structure, or processes that would be necessary to practice the invention, and that would be well known to those of skill in the art, are not necessarily shown and should be assumed to be present unless otherwise indicated.